associate research scientists

Francesco Savelli

Research Interests: Your inner sense of location relative to the external world is a cognitive abstraction of your sensorimotor experience -- something that your brain has to "make up." I study the neural circuits responsible for this process. I combine electrophysiology in behaving animals and computer modeling to investigate the functional properties of the spatial cells of the hippocampal formation, such as place, grid, and boundary cells

assistant research scientists

Xiaojing Chen

Research Interests: Dentate gyrus (DG) is the first step of the entorhinal input information transfer into the hippocampus. I did juxtacellular recording from granule cells or mossy cells in freely moving rats to reveal the different functions of these two dentate principal cell types in navigation. Lateral entorhinal cortex (LEC) is one of the major inputs to the hippocampus, I did tetrode recording from the LEC when rats did a goal oriented task to reveal the firing principles of LEC cells. I am now working on calcium imaging in CA1 of freely moving mice with microendoscopy technique.

Heekyung Lee

Research Interests: The hippocampus plays an important role in memory formation, storage, and retrieval. In particular, the CA3 subregion of the hippocampus has received attention for its potential role in associative memory because of its strong recurrent circuitry. Using electrophysiological approaches, my current research is focused on understanding the neural computation in the CA3 subregion, in both young and aged animals.

Manu Madhav

Research Interests: Manu is a 5th year postdoctoral research fellow. His research interests involve utilizing tools from robotics, control theory and closed-loop experimental approaches to probe and model neural and behavioral circuits in intact, behaving organisms. In the Knierim lab, he is currently working on the dome project that uses an augmented reality apparatus to tease apart the contribution of landmarks and path integrative cues towards forming the hippocampal cognitive map. http://www.manusmad.com

Cheng Wang

Research Interests: Lateral and medial entorhinal cortex are two major inputs to the hippocampus. Using tetrode recordings from rats in different behavior paradigms and novel analysis, I have revealed a fundamental functional double dissociation between the lateral entorhinal cortex (LEC) and the medial entorhinal cortex (MEC), in that LEC encodes spatial information about external objects in egocentric frame of reference whereas MEC encodes spatial information in allocentric framework. I also used computational techniques to help reveal the different functions served by proximal and distal regions of the CA3 transverse axis, i.e., pattern separation and pattern completion, respectively.

graduate students

Doug Goodsmith

Research Interests: The dentate gyrus is thought to be essential for pattern separation, a process necessary for preventing interference between similar memories or experiences. Unlike other hippocampal subfields, the dentate gyrus contains multiple excitatory cell types: granule cells in the granule cell layer and a small number of highly active mossy cells in the hilus. Within the granule cell layer, both mature granule cells and immature adult-born granule cells are present. Due to the close proximity of these distinct dentate gyrus cell types, it has been difficult to differentiate between the activity of dentate cell types using extracellular recordings. Therefore, little is known about the firing properties of cells in the dentate gyrus relative to CA1 or CA3. I am studying the firing properties of mossy cells, mature granule cells, and optogenetically identified adult-born granule cells. By comparing the activity of all excitatory cell types within the dentate gyrus circuit, we hope to determine how each cell type contributes to pattern separation and other dentate functions.

William Hockeimer

Research Interests: Electrophysiological data from the hippocampus has revealed that individual neurons called place cells are active in certain spatial locations and that this activity can be modulated by the the non-spatial, sensory cues present. This has led to a theory called the Cognitive Map Theory which proposes that memories about our experiences are encoded in terms of the locations in which they took place. My project seeks to provide a direct test of an idea regarding how the Cognitive Map could be constructed at the neural level. A hypothesis termed the "rate coding" hypothesis states that the location where a memory took place is encoded in the set of active place cells at the time of encoding and the non-spatial aspects of that memory are encoded in the high-dimensional pattern of firing rates of those neurons. To address the rate coding hypothesis I designed a novel, semi-automated apparatus called Ratterdam. This track features a series of passageways arranged in a city-block grid. Each passageway contains one of three textured floorplates which are swapped among alleys across a day's session such that every alley will contain each floorplate. This allows us to dissociate the spatial and nonspatial responses among hippocampal neurons and test the prediction that a stable place map at a given location will exhibit texture-dependent modulations of firing rate.

Bharath Krishnan

Leo Lee

Master's Student

Research Interests: Uncover the mechanism behind scan-potentiated hippocampal place fields while also developing an optical imaging technique for measuring neuronal activity in freely moving rats. Additionally, it would be interesting to see how analyzing sensory information such as visual input can influence memory formation and consolidation in the hippocampus.

Vyash Puliyadi

Research Interests: The lateral entorhinal cortex is one of the major inputs into the hippocampus and appears to particularly vulnerable in both aging and Alzheimer’s disease. In Alzheimer’s disease, there is significant neuronal loss and synaptic loss observed, early in disease progression. Similar findings have been observed in naturally aged Long Evans rat model of aging. In a collaboration with Michela Gallagher, my work in this area focuses on examining the single-unit activity of neurons in the lateral entorhinal cortex to unveil what kinds of information the lateral entorhinal cortex may conveys to the hippocampus and how it may be altered by the structural and molecular changes that occur during aging.

Chia-Hsuan Wang

Research Interests: From home to school, from bedroom to bathroom, we live within, and move between spatial compartments every day. The world surrounding us is highly-compartmentalized but not discrete: we do not teleport ourselves from one spatial compartment to another; paths that lead us through different rooms, buildings, and districts are always continuous. I am interested in how a segmented yet continuous space can be represented by the cognitive map. Do we develop a gigantic map to preserve the continuity, or do we switch between discrete maps to emphasize individual compartments? Are the boundaries that segregate the environment being encoded by the cognitive map and treated differently from other objects? What types of environmental cues are used to perceptually segregate the environment? My current project focuses on how environments segregated by two-dimensional surface cues (different textures on the floor) are represented by rat place cells. We recorded place cell activities with tetrodes when the rat was foraging in compartmentalized environments, and found that place fields tended to switch on/off near the surface cue boundaries. The finding suggests that flat surface cue boundaries that do not hinder the sight or the movement of the rat are still encoded by the place cell map, and such encoding mechanism decorrelates the neural representations of two neighboring points across the boundary.

undergraduate students

Brian Li

lab staff

Kimberly Nnah

Research Technologist

Geeta Rao

Lab Manager

Research Interests: Intermittent locomotion, exploration consisting of alternating bouts of forward progression and pauses, is a ubiquitously observed behavior. During the pauses in locomotion, rats engage in scanning behavior, consisting of lateral or vertical head movements, presumably to investigate environmental features. We have previously shown that increased neural activity during head scanning predicted the formation and potentiation of place fields on the next pass through that location (Monaco et. al, 2014.) This phenomenon may reflect single-trial encoding of non-spatial information onto a spatial framework, a hallmark of episodic memory. We plan to further characterize scan-related hippocampal place cell firing and field potentiation in hippocampal CA1 and CA3 subfields. We are also currently examining whether changes in scanning behavior and scan-related hippocampal cell firing may contribute to cognitive spatial deficits observed in old animals. Whether scan potentiation of place fields in old animals occurs is a particularly intriguing question that we will be addressing in the near future with further data acquisition. Whether firing during scanning behavior signals particularly salient locations in the environment, such as reward encounters, is a further avenue of investigation.

collaborators

Kim Christian

Research Assistant Professor of Neuroscience, Perelman School of Medicine, University of Pennsylvania

Professor, Department of Biomedical Engineering, Whiting School of Engineering

Katie Hedrick

Ravikrishnan Jayakumar

Research Interests: Ravi Jayakumar is a Ph.D candidate in Prof. Noah Cowan's LIMBS Lab at JHU. His current research focus is on the role that path integration plays in the formation and update of the internal cognitive map. Ravi and Manu Madhav, a post doc from Prof. James Knierim's lab, have been the primary drivers in the design & construction of the Dome, a novel augmented reality experiment apparatus designed at teasing apart this question. Previous work from this project has revealed that the path integrator gain, as revealed by CA1 place cell activity, is highly plastic and is recalibrated by the animal's recent experience with external landmarks and their relationship to the animal's self-motion cues. His path into neuroscience has had unusual origins with a Bachelors in Mechanical Engineering, a stint at an automobile MNC, a Masters specializing in Robotics and eventually joining Prof. Noah Cowan's lab from whom he received training in the mathematical methods of system identification in complex biological systems. Multiple close collaborative projects between Noah & Jim included the combined mentorship of Ravi, leading to this unholy amalgamation of an engineer and neuroscientist.